Which is not a pyramidal molecule ?

Options

A. `NH_3`
B. `PCI_3`
C. `SOCI_2`
D. `ICI_3`

Answer

To determine which molecule is not pyramidal among the given options, we will analyze each molecule's structure, steric number, hybridization, and shape.

### Step-by-Step Solution:

1. **Analyze Option A: NH3 (Ammonia)**
- **Central Atom:** Nitrogen (N)
- **Valence Electrons:** 5 (from nitrogen)
- **Bonds:** 3 single bonds with hydrogen (H) and 1 lone pair.
- **Steric Number Calculation:**
- Steric number = Number of sigma bonds + Number of lone pairs
- Steric number = 3 (N-H bonds) + 1 (lone pair) = 4
- **Hybridization:**
- With a steric number of 4, hybridization is sp³.
- **Geometry:**
- Tetrahedral due to sp³ hybridization.
- **Shape:**
- The presence of a lone pair gives it a trigonal pyramidal shape.
- **Conclusion:** NH3 is a pyramidal molecule.

2. **Analyze Option B: PCl3 (Phosphorus Trichloride)**
- **Central Atom:** Phosphorus (P)
- **Valence Electrons:** 5 (from phosphorus)
- **Bonds:** 3 single bonds with chlorine (Cl) and 1 lone pair.
- **Steric Number Calculation:**
- Steric number = 3 (P-Cl bonds) + 1 (lone pair) = 4
- **Hybridization:**
- With a steric number of 4, hybridization is sp³.
- **Geometry:**
- Tetrahedral due to sp³ hybridization.
- **Shape:**
- The presence of a lone pair gives it a trigonal pyramidal shape.
- **Conclusion:** PCl3 is a pyramidal molecule.

3. **Analyze Option C: SOCl2 (Thionyl Chloride)**
- **Central Atom:** Sulfur (S)
- **Valence Electrons:** 6 (from sulfur)
- **Bonds:** 2 single bonds with chlorine (Cl) and 1 double bond with oxygen (O), plus 1 lone pair.
- **Steric Number Calculation:**
- Steric number = 3 (2 P-Cl bonds + 1 S=O bond) + 1 (lone pair) = 4
- **Hybridization:**
- With a steric number of 4, hybridization is sp³.
- **Geometry:**
- Tetrahedral due to sp³ hybridization.
- **Shape:**
- The presence of a lone pair gives it a trigonal pyramidal shape.
- **Conclusion:** SOCl2 is a pyramidal molecule.

4. **Analyze Option D: ICl3 (Iodine Trichloride)**
- **Central Atom:** Iodine (I)
- **Valence Electrons:** 7 (from iodine)
- **Bonds:** 3 single bonds with chlorine (Cl) and 2 lone pairs.
- **Steric Number Calculation:**
- Steric number = 3 (I-Cl bonds) + 2 (lone pairs) = 5
- **Hybridization:**
- With a steric number of 5, hybridization is sp³d.
- **Geometry:**
- Trigonal bipyramidal due to sp³d hybridization.
- **Shape:**
- The presence of lone pairs leads to a T-shaped structure.
- **Conclusion:** ICl3 is **not** a pyramidal molecule.

### Final Answer:
**D. ICl3 is not a pyramidal molecule.**